The present invention relates to a fuel hose wherein a highly flowable electrically conductive fluororesin layer is used as an inner layer, and the inside surface thereof is substantially smooth even when it is molded at a high speed.
Heretofore, a fluororesin is used in a wide range of fields, since it is excellent in e.g. heat resistance, chemical resistance, weather resistance, non-tackiness, low frictional nature and low dielectric property. For example, use as a surface covering material to cover a substrate is known wherein a film or the like of a fluororesin is laminated on the surface of a substrate made of an inorganic material such as a metal or glass or an organic material such as a synthetic resin. Further, as an important application to a laminate, a fuel hose may be mentioned which is used in an engine room of an automobile and which is exposed to a severe condition such as a high temperature environment.
The fuel hose is a hose for piping, wherein a gasoline fuel containing an alcohol or an aromatic compound is transported. In recent years, regulations relating to permeation of gasoline have become severer, and as a measure to cope with such requirements, a hose of a multilayer structure such as a two layer structure, has been proposed, and especially for the inner layer which is directly in contact with the fuel, it is desired to use a resin having chemical resistance against a corrosive material such as ethanol or methanol present in the fuel and a gas barrier property not to let such a material permeate. From such a viewpoint, a fluororesin having heat resistance, chemical resistance and gas barrier property, is considered to be one of the most preferred materials, as the material for the inner layer.
However, the fluororesin forming the inner layer has a high insulation property, whereby static electricity is likely to form and electrification is likely to result when a fuel passes in the hose. Accordingly, leakage of the fuel due to formation of a hole in the hose, and problems due to electric discharge, are likely to result. Therefore, it is necessary to prevent electrification of the fluororesin, for example, by imparting electrical conductivity to release the formed static electricity.
On the other hand, for the outer layer of a fuel hose, it is common to use a polyamide resin such as polyamide 6, polyamide 11 or polyamide 12, which has relatively good durability.
The present inventors have disclosed in JP-A-10-311461 a fuel hose wherein an outer layer is made of a polyamide thermoplastic resin having an amino group-containing compound, and an inner layer is made of a fluororesin, and wherein the outer layer and the inner layer are bonded with high strength by means of a fluorinated adhesive resin.
At present, in the field of fuel hoses, for the purpose of mass production, it is required to carry out molding at a withdrawing speed for the production of a hose as high as possible, for example, at a withdrawing speed of at least 15 m/min. According to a study by the present inventors, it is considerably difficult to satisfy such a requirement in the case of a hose wherein the outer layer is made of a thermoplastic resin other than a fluororesin, and an inner layer is made of an electrically conductive fluororesin.
Namely, the thermoplastic resin of the outer layer is basically highly melt flowable and can satisfy the requirement, but the problem is the electrically conductive fluororesin of the inner layer, and it is not easy to satisfy the requirement. Namely, the fluororesin is basically a low melt flowable resin, and when an electrical conductivity-imparting filler such as carbon black is incorporated thereto in order to impart an antistatic function, the melt flowability will further be lowered. If high speed molding of a hose is carried out at a withdrawing speed of the above-mentioned high speed, melt fracture (so-called melfra) will form, whereby the inside surface of the form will be roughened, and the appearance will be poor, whereby there has been a problem that the commercial value decreases substantially.
Further, a fuel hose is basically subjected to bending at various angles over the entire length of a straight tube produced by extrusion molding, in order to adapt it to configurational or spacial restrictions in a specific structure of each automobile. The bending of the hose not only increases a process step, but wrinkles may thereby be formed. Once wrinkles are formed, the stress will be concentrated at such a portion, whereby there will be a problem that the useful life of the hose tends to be substantially short.
It is an object of the present invention to solve the above-mentioned problems and to provide a fuel hose comprising an outer layer made of a thermoplastic resin and an inner layer made of a fluororesin having electrical conductivity, and which is excellent in the adhesive strength between the inner and outer layers, wherein the surface smoothness is secured even by molding at a high speed. Further, it is intended to provide preferably a fuel hose which can be mounted on an automobile without necessity of bending processing.